July 14, 2016

Tips on Analgesia in Pregnant and Lactating Dogs and Cats

Pregnant and nursing animals in pain need special consideration because clinical trials of analgesics usually exclude these populations and safety data are lacking.
By Amy Karon, DVM, MPH
Pregnant and nursing animals in pain need special consideration because clinical trials of analgesics usually exclude these populations and safety data are lacking. A few recent review articles and guidelines with helpful information are summarized here. 

Overall Approach to Analgesia

Pregnancy causes physiologic changes that can alter pharmacokinetics and pharmacodynamics, Karol Mathews, DVM, DVSc, noted in an article published in Veterinary Clinics of North America: Small Animal Practice.
 
For example, higher cutaneous blood flow can increase the absorption of topical medications. Dr. Mathews notes. Greater total body water increases the volume of drug distribution, and higher total body fat lowers the plasma availability of lipid-soluble drugs. Changes in liver enzyme activity affect the breakdown of drugs that undergo hepatic metabolism, and increased renal function escalates the elimination of water-soluble drugs and their metabolites.
 
Furthermore, drugs and their metabolites can cross the maternal-fetal barrier and can reach potentially hazardous concentrations in milk. Counterbalancing these risks are the need for humane care and the fact that both chronic and severe acute pain contribute to poor perinatal outcomes. Thus, the risks and benefits of analgesia in pregnant and nursing animals merit case-by-case consideration.
 

Opioids in Pregnant & Nursing Cats & Dogs

Opioids tend to be the analgesic of choice for pregnant dogs and cats. Teratogenicity and other adverse fetal effects are generally not a concern, except in the rare case that a patient needs long-term opioids, according to Dr. Mathews.
 
The World Small Animal Veterinarian Association (WSAVA) recommends hydromorphine and morphine over meperidine, butorphanol, or nalbuphine, which are more lipid-soluble, and therefore can reach higher concentrations in the fetus.
 
Perhaps the most common use of opioids in pregnant animals is before cesarean section. Most newborns do not show adverse effects with this use, but if they seem depressed, WSAVA recommends placing a drop of naloxone under the tongue. Dr. Mathews recommends repeating this dose in 30 minutes if the depression persists.
 
For lactating animals that need ongoing opioids, nursing should be timed for just before the next dose, and opioids with long half-lives should be avoided, according to Dr. Mathews.
 

Local Anesthetics in Pregnant & Nursing Cats & Dogs 

Local anesthetics are generally considered safe and non-teratogenic, and can be a good alternative to systemic analgesia, according to WSAVA. For example, local infiltration of the cesarean incision line can reduce the need for systemic analgesia. Because lidocaine and its metabolites are not lipophilic, concerns about concentration in milk are minimal, WSAVA notes.
 

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